In a stimulation treatment of a subterranean reservoir, such as during hydraulic fracturing, a fluid is pumped into well which penetrates the reservoir at a pressure which is sufficient to create or enlarge a fracture within the reservoir. During fracturing, vertical fracture faces are held apart by the friction pressure created by the flow of the fracturing fluid. However, when the treatment ends and this friction pressure are no longer present, the fracture opening closes under the influence of tectonic stresses.
Productivity of a hydraulic fracturing treatment operation is dependent on the effectiveness of the propping agent present in the fracturing fluid. The proppant serves to prevent the fracture from closing and to hold the faces of the reservoir apart after the pumping treatment is completed. The success in keeping the fracture from closing is dependent on the strength and distribution of the proppant. Typically, the proppant bed that fills the fracture has a fluid conductivity which is hundreds of times greater than the formation. Thus, the proppant filled channel increases the effective drainage radius of the wellbore and increases the producing rate of the well.
However, beds composed of conventional proppants, such as sand, typically exhibit low flow capacity even though they provide support to hold the fracture faces apart for flow to occur between the beds.
When fracturing low-permeability reservoirs are drilled on large spacing it is advantageous to create long propped fractures. Usually, such treatments are performed using viscous fluids that are capable of transporting proppant far into the fracture with a minimum of settling. However, in order to create such long fracture lengths, a large amount of proppant and a large volume of viscous fluid are required.
Alternative methods include the use of a less viscous fluid and a proppant with a small particle size. Since fine proppant tends to slowly settle from its transport fluid, the fluid can be carried over long distances. However, proppant of small particle size has an extremely low flow capacity and a suitable C/ki ratio (the ratio of fracture conductivity to formation permeability) is often unlikely. Thus, this method is often unsatisfactory.
It should be understood that the above-described discussion is provided for illustrative purposes only and is not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. Thus, none of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude each or any of the above-cited features or disadvantages merely because of the mention thereof herein.
Accordingly, there exists a need for a method for effectively propping low permeability reservoirs where long propped fractures are required and having one or more of the attributes or capabilities described or shown in, or as may be apparent from, the other portions of this patent.